7.4 Reading: Planetary boundaries

 

7.4 Reading: Planetary boundaries

 

1.      What are the nine planetary boundaries?  These nine planetary boundaries are  

·       Climate change (CO2 concentration in the atmosphere <350 ppm and/or a maximum change of +1 W m-2 in radiative forcing);

·       Ocean acidification (mean surface seawater saturation state with respect to aragonite ≥ 80% of pre-industrial levels);

·       Stratospheric ozone (<5% reduction in O3 concentration from pre-industrial level of 290 Dobson Units);

·       Biogeochemical nitrogen (N) cycle (limit industrial and agricultural fixation of N2 to 35 Tg N yr-1) and phosphorus (P) cycle (annual P inflow to oceans not to exceed 10 times the natural background weathering of P);

·       Global freshwater use (<4000 km3 yr-1 of consumptive use of runoff resources);

·       Land system change (<15% of the ice-free land surface under cropland);  

·       Biological diversity is lost (annual rate of <10 extinctions per million species).

·       Chemical pollution

·       Atmospheric aerosol loading.

 

2.      Which boundaries have been transgressed?  Humanity has already transgressed 3 planetary boundaries as follow:  climate change, rate of biodiversity loss, and changes to the global nitrogen cycle.

3.      What are the risks of overshooting these and other planetary boundaries?   Crossing the threshold of the planetary boundaries of the earth system would lead to risk of environmental disaster, and threat to humanity and survival. Scientists have provided warning for the transgressing planetary boundaries of the earth system such as climate change.

of deleterious or even catastrophic environmental. Many environmental changes have occurred and evident during the Anthropocene era that how it showed in the Holocene time.

 

4.      To what extent might the concept of ‘planetary boundaries’ be controversial or problematic, and to whom? The planetary boundaries will become deleterious when it crosses the threshold of the proper functioning of the earth system. And this will affect humanity